Firefox Add-ons
- Tab Mix Plus
- Adblock Plus
- Flashblock
- Mouse Gestures
- MultiSidebar
- Vertigo
- PDF Download
- del.icio.us Complete
- Google Browser Sync
- Digger
- Dom Inspector
- Firebug
- Live HTTP Headers
- Tamper Data
- User Agent Switcher
- View Cookies
- Web Developer
- YSlow
More add-ons can be found at addons.mozilla.org